Chapter 21 Electromagnetic Induction and Faraday's Law

21.5 Electric Generators
A generator is the opposite of a motor – it
transforms mechanical energy into electrical
energy. This is an ac generator:
The axle is rotated by an
external force such as
falling water or steam.
The brushes are in
constant electrical
contact with the slip
rings.
21.5 Electric Generators
A dc generator is
similar, except that it
has a split-ring
commutator instead of
slip rings.
21.5 Electric Generators
=
ab ⊥
=
2 B N l v 2 B N l v sinθ
ab
21.5 Electric Generators
A sinusoidal emf is induced in the rotating
loop (N is the number of turns, and A the area
of the loop):
21.7 Transformers and Transmission
of Power
A transformer consists of two coils, either
interwoven or linked by an iron core. A
changing emf in one induces an emf in the
other.
The ratio of the emfs is equal to the ratio of
the number of turns in each coil:
(21-6)
21.7 Transformers and Transmission
of Power
This is a step-up
transformer – the emf
in the secondary coil
is larger than the emf
in the primary:
Why is the iron core
laminated?
4